1. Field of the Invention
The present invention generally relates to such a cooling unit for air conditioners that is furnished with a drain case suitable for efficiently draining the condensed water generated on the surface of a refrigerant evaporator housed within a unit case, by way of examples. More particularly, the present invention is related to the drain case for the cooling unit for air conditioners.
2. Description of the Related Art
As illustrated in FIGS. 26 and 27, there has conventionally been an air conditioner which houses a refrigerant evaporator 102 within a recessed part 101 of a unit case 100 serving as a duct for sending the air into a vehicle compartment. In this air conditioner, a drain port 103 is formed at the bottom wall part of the recessed part 101, which drain port 103 being opened under the refrigerant evaporator 102, to drain the condensed water adhered to the surface of the refrigerant evaporator 102 from the unit case 100 to outside.
On the other hand, as illustrated in FIG. 28, the refrigerant evaporator 102 has been composed by stacking a plurality of plural pairs of formed plates 106 with which refrigerant passage pipes 104 and two pieces of tank parts 105 are integrally formed at the end part side of the refrigerant passage pipes 104. A core part 107 of the refrigerant evaporator 102 is so composed that fins 108 are disposed between the adjacent refrigerant passage pipes 104.
The air side heat transmission surface of the refrigerant evaporator 102 (the surface to which the condensed water adheres) is formed from the surfaces of the fins 108 and the surfaces of the refrigerant passage pipes 104. As illustrated in FIG. 29, the condensed water adhered to the surface of the fins 108 flows along the fins 108 to the side of the refrigerant passage pipes 104. On the other hand, as illustrated in FIG. 30, a plurality of inclined ribs 109 are formed in the protruded state at the inside of the refrigerant passage pipes 104 (in the recessed state at the air side heat transmission surface) to improve the heat transmission efficiency. The condensed water flows along the inclined ribs 109 to the lower end side of the core part 107. Based on the principle of draining the condensed water as described in the above, the condensed water adhered to the surfaces of the fins 108 and refrigerant passage pipes 104 is drained to the lower end side of the core part 107. Incidentally, a folded part 113 prevents the fins 108 from buckling.
There are two types of surface treatments for refrigerant passage pipes 104 formed by a pair of plates 106 and the fins 108; one is hydrophilic treatment, and the other is water repellent treatment. Hitherto, the hydrophilic treatment has generally been employed for two reasons; there has been no water repellent treatment liquid which can withstand the operational environment of the refrigerant evaporator 102, and when the water repellent treatment is applied to the surface of the refrigerant passage pipes 104 and fins 108, water drops are generated on the surfaces of the refrigerant passage pipes 104 and fins 108. As illustrated in FIG. 31, when the fins 108 are provided with louvers 110, the water drops may be repelled by and between the louvers 110 and stay there or may not flow downwards from the surfaces of the fins 108 but may splash towards the lee side of the unit case 100.
When the hydrophilic treatment is applied to the surfaces of the refrigerant passage pipes 104 and fins 108, water films are formed on the surfaces of the refrigerant passage pipes 104 and fins 108, which serves to supplement the above-described draining principle. As a result, there is no excessive stay of the condensed water, though a water film of approximately 0.1 mm in thickness is formed at the upper end side of the core part 107 due to the effects of the hydrophilic treatment. In the refrigerant evaporator 102 including two pieces of tank parts 105 as illustrated in FIG. 26 at the upper end side of each refrigerant passage pipe, even if the condensed water stays at the lower end part of the refrigerant passage pipes 104, corrosion which may occur at the lower end side of the refrigerant passage pipes 104 is not so significant due to the effects of the sacrificially corroded fins 108.
However, in the refrigerant evaporator 102 in which two pieces of tank parts 105 illustrated in FIG. 27 are formed at the lower end side of the refrigerant passage pipes 104, as there is no fin 108 provided at the lower end side of the refrigerant passage pipes 104 where the condensed water stays, there would be no effect of the sacrificially corroded fins 108. For this reason, localized corrosion which may occur at the lower end side of the refrigerant passage pipes 104 due to the stay of the condensed water is importantly pointed out.
In other words, as illustrated in FIGS. 32 and 33, at the lower end side of the core part 107 or tank parts 105 of the conventional refrigerant evaporator 102, there has been a problem that the drainage of the condensed water adhered to the surfaces of the refrigerant passage pipes 104 and fins 108 is so low that the condensed water stays there. Furthermore, when the refrigerant evaporator 102 in this arrangement is inserted into the unit case 100, the drainage of the refrigerant evaporator 102 is worsened by the water contained in an insulator 111 disposed between the unit case 100 and the lower end part of the refrigerant evaporator 102, by way of examples.
The reason for the above is, as illustrated in FIG. 34, the condensed water flowed from the lee side end part A of the lower end parts of the two pieces of tank parts 105 easily flows along the unit case 100 into a drain port 103, while the condensed water flowed from the windward side end part B of the lower end parts of the two pieces of tank parts 105 bridges the clearance between the lower end parts of the tank parts 105 and the insulator 111 and stays there (water stay part 112).
When the condensed water flowed from the lower end part center C between the two pieces of tank parts 105 flows to the windward side end part B side of the lower end parts of the two pieces of tank parts 105, the condensed water joins the water drops in bridging and is held at the stay part 112. Alternatively, when the same condensed water flows to the lee side end part A side of the lower end parts of the two pieces of tank parts 105, the condensed water stays at the stay part 114 due to no guiding means available into which the condensed water falls.
In the water drops staying at the stay parts 112 and 114, (water retention force due to surface treatment)+(structural difficulty in dropping of water drops)&gt;(gravity on water drops) is established. Therefore, the water drops are held at the stay parts 112 and 114, and drops downwards as the water drops grow.
As described in the above, in the refrigerant evaporator 102 in which the two pieces of tanks 105 are formed at the lower end side of the refrigerant passage pipes 105, there has been a problem that the condensed water easily stays and localized corrosion is easily occur at the lower end side of the refrigerant passage pipes 104 where corrosive elements (Cl, NOx, etc.) in the atmosphere are easily condensed.